Abstract : This paper introduces a constant pressure water supply system based on FXzNPLC and FR-A500 frequency converter control, which has two major subsystems: domestic constant pressure water supply and fire constant pressure water supply. The system design scheme is analyzed in detail, the system composition and working principle are explained, a detailed system wiring diagram is given, and the parameter setting and adjustment of FR-A500 frequency converter PID control are analyzed. Keywords : constant pressure water supply system; PLC; frequency converter; PID control 0 Introduction The constant pressure water supply technology based on PLC and frequency converter control has significant energy-saving benefits, complete control and protection functions, soft start and soft stop of the unit, wide input voltage range, small electromagnetic shock, and flexible and convenient switching of water pump motor operation combination compared with traditional technology. It is currently widely used in water plant water delivery pumping stations, secondary pressurization stations, industrial boiler water supply, community and high-rise building water supply, and other industrial water supply fields. [b]1 System Design 1.1 System Circuit Design[/b] (1) Working power supply electrical control circuit. This system includes a PLC and inverter power supply relay control circuit (see Figure L). The power supply to the PLC and inverter is controlled by buttons, and a power supply indicator light is provided. In practical applications, a manual start and stop relay control circuit for the water pump should also be included. This allows for manual control of the water pump in case of inverter or PLC failure, ensuring continuous operation of the water supply system. [b][align=center]For more details, please click: Design of Intelligent Community Water Supply System Based on PLC and Inverter Control[/align][/b]